Electrochemical hydrogen compressor

ABSTRACT

The invention disclosed relates to an apparatus and process for electrochemical compression of hydrogen. The apparatus comprises a membrane electrolyte cell assembly (MEA), including planar gas distribution plates sandwiching the MEA, the assembly being held together by end-plates, the end-plates having complementary peripheral grooves for seating an intervening seal between the end-plates and the MEA, the end-plate on the anode side further including a hydrogen supply inlet and the end-plate on the cathode side further including a compressed hydrogen outlet. Both single cell and multi-cell assemblies are disclosed. The multi-cell assemblies comprise a plurality of such single cells connected in series, such that the compressed hydrogen from the outlet of a first cell is connected to the hydrogen outlet of the next cell in series, where each cell is electrically isolated from the adjacent cell in the series. The process involves the electrochemical compression of hydrogen in such cells, whereby pressures of up to 12,000 psi are achieved by multi-cell assemblies.

BACKGROUND OF THE INVENTION

[0001] This invention relates to an apparatus and process forelectrochemical compression of hydrogen.

[0002] Fuel cells offer an environmentally friendly method of efficientenergy generation, and the use of hydrogen as the fuel of choice isattractive as the conversion to electrical energy is emissions-free,with water and heat being the only by-products. The delivery of hydrogenin gaseous or liquid form or as an absorbed species (e.g. metal hydride,on activated carbon, or in carbon nanotubes) depends on the fuel cellapplication, and re-fueling frequency and related autonomy are importantfactors to consider in the selection of the appropriate mode of fuelstorage. As liquid hydrogen involves energy-intensive and sophisticatedcryogenic technologies and has a high boil-off rate and absorptiontechnology is still in its infancy, gaseous hydrogen is a convenient andcommon form for storage, usually by pressurized containment forincreased energy density. To this end, mechanical compression is themost common means by which to achieve pressurization; however, itsuffers from limitations due to 1) intensive energy use, 2)wear-and-tear of moving parts, 3) hydrogen embrittlement, 4) excessivenoise, 5) bulky equipment, and 6) contamination of the gas usually bycompressor lubricants. Non-mechanical pressurization by thermal cyclingis possible, but this is also energy intensive and not commerciallypractical yet.

[0003] Electrochemical transfer of hydrogen through proton-conductivematerials is known, and fundamental studies on single-stage transferapplications can be found reported in the literature. For example, theuse of thin perovskite-type oxide proton-conducting ceramics is welldocumented for single-stage separation of hydrogen from gas mixtures[1-3]. In these applications, the single cell operates at elevatedtemperatures (500-1000° C.) in order to maintain sufficiently highprotonic conductivity through the separator. Reports on electrochemicalhydrogen compression are scarce and most describe the use of singlecells with a polymer electrolyte membrane (PEM), i.e. Nafion®, as theproton-conductive separator and Pt as the electrocatalyst on carbonelectrodes (both anode and cathode) [4-7]. Operation of these cells topressure differentials of ˜43 atm (with anodic compartment pressure=1atm) occurs without excessive energy demands; at greater differentials,however, rapid loss of H₂ due to leakage around the cell seals causes anexponential increase in power consumption. Use of Nafion PEM inelectrochemical transfer of H₂ has also been reported [8]; in this case,H₂ was directed to the cathodic compartment filled with water in orderto de-oxygenate the water by reaction of the H₂ with the dissolved O₂.It is important to note that in all these applications, electrochemicaltransport is selective to H₂ only due to the proton conductive nature ofthe separator and, in a gas mixture, hydrogen is not only concentrated(pressurized) but also purified by such means.

[0004] In U.S. Pat. No. 6,361,896 of Eberle et al. [10], the disclosureindicates that for single cell devices, differential pressures of up toabout 10 bar can be achieved. This compares with earlier prior artdevices that can only achieve a 5 bar differential pressure. Alsodisclosed is the use of a second cell to increase the differentialpressure theoretically to “more than about 15 bar”. The higher pressuredifferential is said to be achieved by means of a planar porous gasdistribution support layer on the anode side (see col. 2). However, itis significant that there is no experimental proof provided that thiswas achieved. Moreover, no specific structure is described

[0005] Also described in Ströbel et al. [5] is a multi-cell stack. It isnoted that the cells in the stack are connected in-parallel, so thatthere is no H₂ transport from one cell to the next. Accordingly, the H₂output pressure from each cell is the same. The maximum pressuredifferential achieved was about 54 bar.

SUMMARY OF THE INVENTION

[0006] According to the invention, an apparatus and process are providedfor pressurizing hydrogen electrochemically.

[0007] As will be discussed later, this technology targets the hydrogensupply and gas storage industries as well as the emerging fuel cellindustry. With potential application of the technology in the fuel cellindustry, high-pressure compression is desired and, more specifically,pressurization up to 12,000 psi is targeted, as this level is deemednecessary by the transportation industry for practical implementation offuel cell vehicles.

[0008] According to one aspect of the invention, an apparatus isprovided for compression of hydrogen, comprising a membrane electrolytecell assembly (MEA), including a proton-conducting electrolyte membrane,an anode on one side of the membrane and a cathode on the other side ofthe membrane, the anode having an electrochemically active material foroxidizing hydrogen to protons, the cathode having an electrochemicallyactive material for reducing protons to hydrogen, and further comprisingnext to the anode and cathode, planar gas distribution and supportplates sandwiching the MEA, the assembly being held together byend-plates, the end-plates having complementary peripheral grooves forseating an intervening seal between the end-plates and the MEA, theend-plate on the anode side further including a hydrogen supply inletand the end-plate on the cathode side further including a compressedhydrogen outlet.

[0009] According to another aspect of the invention, a process isprovided for the compression of hydrogen by means of the apparatusdescribed in the preceding paragraph, wherein hydrogen is compressedelectrochemically by the MEA cell by oxidation of the hydrogen toprotons at the anode, which having passed through the membrane to thecathode side are reduced back to hydrogen and discharged under pressure.

[0010] According to yet another aspect of the invention, in order toachieve even higher total or system pressure, we provide a plurality ofsuch cells connected in series. The more cells connected in series, thehigher the final outlet (overall) pressure that is achieved. Byconnection in series, we mean connected such that there is a progressiveincrease in pressure from cell to cell in the series. It would beexpected by those skilled in the art that compression to higherpressures than those achievable by a single cell design according to ourinvention are achievable by including additional cells connected inseries. For example, by setting a pressure differential of 1000 psi perstage (at each cell), compression to 10,000 psi overall would requireten cells.

BRIEF DESCRIPTION OF THE DRAWING

[0011]FIG. 1 is a diagram showing the concept of electrochemicalhydrogen compression.

[0012]FIG. 2 is a diagram showing the concept of multi-stageelectrochemical hydrogen compression.

[0013]FIG. 3 is a concept diagram showing a cross-sectional view of amulti-stage electrochemical hydrogen compressor with an overallcylindrical configuration.

[0014]FIG. 4 is a diagram showing the design of planar gas distributionand support plates according to the invention with complementary groovesfor intervening seals to provide a leak-free seal between the MEA andthe plates.

[0015]FIG. 5 is a diagram showing the unassembled view of a single-stageelectrochemical hydrogen compressor unit according to the invention.

[0016]FIG. 6 is a schematic circuit design for a two-stageelectrochemical hydrogen compressor system according to the invention.

[0017]FIG. 7 is a graph showing the results of electrochemical hydrogencompression to 45 psia (T=22° C.; i=0.6 A).

[0018]FIG. 8 is a graph showing the results of electrochemical hydrogencompression to 75 psia (T=22° C.; i=0.6 A).

[0019]FIG. 9 is a graph showing the voltage applied duringelectrochemical hydrogen compression to 45 psia (T=22° C.; i=0.6 A)(---ΔE derived using equation 4).

[0020]FIG. 10 is a graph showing the voltage applied duringelectrochemical hydrogen compression to 75 psia (T=22° C.; i=0.6 A)(---ΔE derived using equation 4).

[0021]FIG. 11 is a graph showing the voltage applied duringelectrochemical hydrogen compression to 45 psia (T=65° C.; i=0.6 A)(---ΔE derived using equation 4).

[0022]FIG. 12 is a graph showing the voltage applied duringelectrochemical hydrogen compression to 45 psia (T=80° C.; i=0.6 A)(---ΔE derived using equation 4).

[0023]FIG. 13 is a graph showing the voltage applied duringelectrochemical hydrogen compression to 45 psia (T=65° C.; i=0.1 A)(---ΔE derived using equation 4).

[0024]FIG. 14 is a graph showing the results of dual-stage,electrochemical hydrogen compression to 75 psia (T=22° C.).

[0025]FIG. 15 is a graph showing the voltage applied during dual-stage,electrochemical hydrogen compression to 75 psia (T=22° C.) (---ΔEderived using equation 4).

[0026]FIG. 16 is a graph showing the results of electrochemical hydrogencompression to 535 psia (T=22° C.; i=0.6 A).

[0027]FIG. 17 is a graph showing the voltage applied duringelectrochemical hydrogen compression to 535 psia (T=22° C.; i=0.6 A)(---ΔE derived using equation 4).

[0028]FIG. 18 is a graph showing the results of dual-stage,electrochemical hydrogen compression to 2000 psia (T=22° C.).

[0029]FIG. 19 is a graph showing the voltage applied during dual-stage,electrochemical hydrogen compression to 2000 psia (T=22° C.) (---ΔEderived using equation 4).

DETAILED DESCRIPTION OF THE INVENTION

[0030] Electrochemical compression of hydrogen is accomplished by theapplication of an electric potential across a proton-conductive polymerelectrolyte material separating anode and cathode compartments to effectthe transport of hydrogen from one side to the other. The process isbased on the following anodic and cathodic reactions:

H₂→2H⁺+2e⁻ anodic (oxidation)  (1)

2H⁺+2e⁻→H₂ cathodic (reduction)  (2)

[0031] The use of electrocatalysts facilitates these reactions, and theprinciple of operation can be illustrated as shown in FIG. 1. Oxidationof H₂ at the anode 10, located in anodic compartment 12 generateshydrogen ions (protons) and electrons; the hydrogen ions migrate acrossthe proton-conductive polymer electrolyte separator 14 while theelectrons travel via an external circuit to the cathodic compartment 16where reduction back to H₂ takes place at the cathode 18. Fromthermodynamic considerations using the Nemst equation, the theoreticalapplied potential to effect a desired final pressure of H₂ exiting thecathodic compartment can be determined. For example, the thermodynamiccell potential is represented by the following equation: $\begin{matrix}{E_{cell} = {{E_{c} - E_{a}} = {E_{cell}^{\circ} - {\frac{RT}{2F}\quad \ln \quad \frac{a_{H_{2},c}}{a_{H_{2},a}}}}}} & (3)\end{matrix}$

[0032] E_(cell)=thermodynamic cell potential, V

[0033] E_(c)=cathode half-cell potential, V

[0034] E_(a)=anode half-cell potential, V

[0035] E_(cell)°=thermodynamic cell reference potential, 0.00 V

[0036] a_(H) ₂ _(,c)=activity of H₂ at the cathode

[0037] a_(H) ₂ _(,a)=activity of H₂ at the anode

[0038] R=gas constant, 8.3144 mol⁻¹ K⁻¹ L kPa

[0039] T=temperature, K

[0040] F=Faraday constant, 96487 C/mol e⁻

[0041] With hydrogen as a gas, a_(H) ₂ equates to pressure, P_(H) ₂ ,and the applied potential, ΔE, is determined from the followingequation: $\begin{matrix}{{{applied}\quad {potential}} = {{\Delta \quad E} = {{E_{cell}} = {\frac{RT}{2F}\quad \ln \quad \frac{P_{H_{2},c}}{P_{H_{2},a}}}}}} & (4)\end{matrix}$

[0042] For a more rigorous mathematical treatment, the thermodynamicproperty, fugacity (f), is used and is the effective pressure when thenon-ideality of gases is taken into consideration. Fugacity relates to Pby the following equation:

fugacity, f=φP  (5)

[0043] where φ is the fugacity coefficient, akin to the activitycoefficient (γ) in the thermodynamic treatment of non-ideal solutions.Fugacity coefficients have been tabulated for a number of gases and, forhydrogen, φ is essentially 1.0 for pressures up to 1000 psia (68 atm)[9]; at higher pressures, f becomes significant. The applied potentialis then determined more accurately from the following equation:$\begin{matrix}{{{applied}\quad {potential}} = {{\Delta \quad E} = {{E_{cell}} = {{\frac{RT}{2F}\quad \ln \quad \frac{f_{H_{2},c}}{f_{H_{2},a}}} = {{\frac{RT}{2F}\quad \ln \quad \frac{\varphi_{H_{2},c}}{\varphi_{H_{2},a}}} + {\frac{RT}{2F}\quad \ln \quad \frac{P_{H_{2},c}}{P_{H_{2},a}}}}}}}} & (6)\end{matrix}$

[0044] φ_(c)=cathodic compartment fugacity coefficient

[0045] φ_(a)=anodic compartment fugacity coefficient

[0046] For example, for a ten-fold increase in pressure with P_(H) ₂_(,a)=1 atm and P_(H) ₂ _(,c)=10 atm at room temperature (25° C.), theapplied potential is ΔE=29.7 mV (with (φ_(H) ₂ _(,a)=1.000 and φ_(H) ₂_(,c)=1.006). For a further ten-fold increase with P_(H) ₂ _(,a)=10 atmand P_(H) ₂ _(,c)=100 atm, ΔE=30.3 mV (φ_(H) ₂ _(,a)=1.006 and φ_(H) ₂_(,c)=1.063) and, with P_(H) ₂ _(,a)=1 atm and P_(H) ₂ _(,c)=100 atm,ΔE=59.9 mV (φ_(H) ₂ _(,a)=1.000 and φ_(H) ₂ _(,c)=1.063). As evident, arelatively small applied potential results in significantpressurization, and the device functions essentially as a concentrationcell. In actuality, the required applied voltage, E_(working), would behigher due to electrode overpotentials and resistance (circuit and ohmicdrop across the separator) and due to application of an electric currentto effect a timely increase in pressure:

E _(working) =ΔE+E _(polarzation)

E _(polarization)=|η_(a)|+|η_(c) |+iR _(separator) +iR _(circuit)  (7)

[0047] η_(a)=overpotential of the anode, V

[0048] η_(c)=overpotential of the cathode, V

[0049] i=applied current, A

[0050] R_(separator)=resistance across the proton-conductive separator,ohm

[0051] R_(circuit)=resistance of the electrical circuit, ohm

[0052] The overpotentials of the anode and cathode represent chemicalkinetic barriers, i.e. the energy required for electron transfer duringthe anodic and cathodic electrochemical reactions, and the use ofelectrocatalysts (e.g. Pt) and/or higher temperatures can reduce thesevalues. For resistance, the ohmic drop across the separator can beminimized, for instance, by the use of thinner materials and, across thecircuit, with appropriate electrical materials.

[0053] With the initial condition, P_(H) ₂ _(,a)=P_(H) ₂ _(,c)=P_(i),the energy consumption for single-stage compression, from P_(H) ₂_(,c)=P_(i) to P_(f), can be determined from the following equation:$\begin{matrix}{{energy} = {w = {{\Delta \quad {nRT}\quad \ln \quad \frac{P_{f}}{P_{i}}} + {{E_{polarization}(i)}( {\Delta \quad t} )}}}} & (8)\end{matrix}$

[0054] Δn=no. of moles of H₂ transferred, mol

[0055] Δt pressure increase time period, sec

[0056] ΔnRTln(P_(f)/P_(i))=w_(t), thermodynamic work of compression,

[0057] The efficiency (%) of electrochemical hydrogen compression isreferenced to the applied voltage and is a measure of the deviation fromthermodynamic work: $\begin{matrix}{{efficiency} = {\frac{w_{t}}{w} \times 100}} & (9)\end{matrix}$

[0058] In practice, multi-stage compression is preferred forhigh-pressure applications whereby pressure differentials between stagescan be set to reasonable values in order to accommodate materiallimitations (e.g. structural integrity, effective sealing, and H₂back-diffusion phenomenon [5]). For an electrochemical compressor with Nstages with P₁, P₂ . . . P_(N) initially established and kept constant(FIG. 2), the total energy consumption can be determined simply fromsummation of the compression energies at each stage: $\begin{matrix}{{{total}\quad {energy}} = {{\sum\limits_{1}^{N}w_{N}} = {\sum\limits_{1}^{N}{{E_{polarization}^{N}(i)}( {\Delta \quad t} )}}}} & (10)\end{matrix}$

[0059] Methodology

[0060] The design of an electrochemical hydrogen compressor is similarto that of a fuel cell, and it is proposed that a multi-stage unit bemodeled after a PEM fuel cell stack. Nafion® is employed as theproton-conductive polymer membrane separator with Pt as theelectrocatalyst dispersed on carbon to function as the anode and cathodeelectrodes in the overall membrane-electrode-assembly (MEA).

[0061] As shown in FIG. 3, an overall cylindrical multi-cell stackconfiguration, having, for example, hemispherical end-plates 26 providesgood mechanical stability. Hydrogen supply inlet 33 is provided in theend-plate on the anode side of the first cell and compressed hydrogenoutlet 35 in the other end-plate on the cathode side of the last cell.The plates are connected by tie-bolts 28. The design of a multi-stageunit is as illustrated where electrically non-conductive separators 20ensure electrical separation of compression stages. It will beappreciated by those skilled in the art that other configurations willalso work effectively. As with fuel cells, graphite support plates 22could be used sandwiching the MEA's 24, but these require separatecharge collectors for good electrical conductivity (cf. copper endplatesin a fuel cell stack).

[0062] As best seen in FIG. 4, porous stainless steel support plates 22are used, which are positioned adjacent to the MEA 24 with seals (e.g.in the form of an elastomeric o-ring) disposed in grooves 30 to ensure aleak-free seal between the plate and the membrane of the MEA (i.e. theperipheral area outside of the active area). Unlike a fuel cell stack,complex serpentine flow fields are not necessary, and access of H₂ tothe MEA's is simply achieved by perforating the plates 22 e.g. in acentral area 23 of the plate, or by use of sintered frit plates. Thesintered metal frit plates are made of a powdered metal material such asstainless steel, which is compressed into the form of a plate. Suchmaterial provides a structurally strong, yet porous material to providefor passage of gases to and from the active area of the MEA.

[0063] It is believed that the high differential pressures are achievedby means of the porous supporting plate 22 on the anode side and itsseating in socket 25 a. On the cathode side, the porous plate maintainscontact during pressurization with the active area of the MEA via use ofa spring means, including a spring 29 and spring support 31, (i.e. seeFIG. 5) for ensuring adequate electrical contact. High-pressurestability is provided because the plates 22 immobilize the MEA duringpressurization, such that the membrane does not rupture due to aballooning effect.

[0064] Commercially available materials (MEA, stainless steel plating,and seals) are used in the construction of single- and two-stagecompressors (see later). Examples of other proton-conductive membranesinclude sulfonated-polystyrene and the partially fluorinated ionomericmembranes, IonClad R-1010 and R-4010 (Pall Co.), as these represent moreeconomical alternatives to Nafion. Also, as H₂ is the only species ofinterest, complications of slow membrane deterioration, as reported infuel cells and attributed to the formation of hydrogen peroxide (fromreaction of H₂ with O₂) within the membrane, is not expected to be aproblem, and the use of non-fluorinated materials such assulfonated-polystyrene will suffice in electrochemical compressionapplications.

[0065] The design of supporting plates 22 incorporates porosity orperforation characteristics in order to allow sufficient exposure of H₂to catalytic active sites on the surface of the MEA and, at the sametime, permit the plates to give sufficient structural support to themembrane, thus minimizing its deformation under conditions ofhigh-pressure differentials.

[0066] In the embodiment shown in FIGS. 3 and 4, the design of thesupporting plates 22 also incorporates complementary peripheral grooves30 for disposition of seals, e.g. an elastomeric o-ring to insure aleak-free seal between the MEA and the plates.

[0067]FIG. 5 shows the unassembled view of a single stage of the workingsystem responsible for establishing proof-of-concept, multi-stageelectrochemical compression. This electrochemical compressor unitcomprises a membrane-electrode-assembly (MEA) 24 supported by stainlesssteel sintered frit plates 22 a and contained within cylindricalstainless steel housing 26 that make up the anodic and cathodiccompartments. The stainless steel housing 26 is a high-pressure filterholder (Fisher Scientific, cat. no. 09-753-13M) adapted for its presentuse. The membrane-electrode-assembly 24 (Palcan Fuel Cell Co. Ltd.,Vancouver, Canada) is circular in design (FIG. 4) with an active area of11.34 cm² and comprises of gas-diffusion electrodes (anode and cathode),comprising Pt (1 mg/cm²) as the electrocatalyst supported on carbon (40wt. % Pt/C), and Nafion® 115 as the electrolyte. Use of this unit isdocumented in examples described below for single- and dual-stagehydrogen compression.

[0068] As shown in FIG. 5, complementary pairs of grooves 25 and pocket25 a are machined into the inside face of both end-plates 26. Uponassembly, the seal between the end-plates 26 and the MEA 24, is providedby an o-ring 27 of an elastomeric material, disposed in the grooves 25,and the frit plate 22 a is seated in pocket 25 a.

[0069] A spring 29 and spring support 31 are provided on the cathodeside. Both the spring and spring support are conveniently made ofstainless steel. This spring and spring support arrangement provides forequalization of the force exerted on the MEA by the frit plate on thecathode side of the MEA 24, regardless of the pressure differentialacross the MEA, such that the MEA can move together, i.e. withoutseparating as a result of the high pressure.

[0070] As H₂ is a small molecule able to permeate through many types ofmaterials, the selection and design of appropriate sealing material isimportant. Examples include Viton®, Santoprene®, and PTFE.

[0071] The multi-stage compressor embodiment includes a plurality of PEMcells connected in series, such that the compressed hydrogen from theoutlet of a first cell in the series is fed to the hydrogen inlet of thenext cell in series, wherein each cell is electrically isolated from theadjacent cell in the series. Note that while it is apparent that in theStrobel et al. publication, the cells are clearly shown to be connectedin parallel, U.S. Pat. No. 6,361,896 states that the cells are connected“in series”. However, it is apparent that by “in series” the authorsmean that the cells are arranged or placed adjacent to each other, i.e.as illustrated in the publication, for increased hydrogen flux. However,the hydrogen outputs and inputs are not connected in series and,therefore, progressive increases in pressure from cell to cell are notpossible.

[0072] The circuit diagram for a two-stage unit connected in seriesshowing the balance-of-plant is illustrated in FIG. 6, wherein PG refersto pressure gauges; PCV refers to pressure check valves; CV refers tocheck valves; FM refers to flow meters; PT refers to pressuretransducers; HUM refers to the gas humidifier; HTR refers to the heater;RH refers to the relative humidity ports; and T/C refers to thethermocouple ports. Separate power supplies are used for eachelectrochemical compressor unit. The system is purged with nitrogenprior to hydrogen compression. Hydrogen is humidified by HUM101 andinitially introduced to the entire system at atmospheric pressure.Thereafter, power is applied to the electrochemical compressor unit(s),and the pressure is monitored via PT101, PT102, and PT103. The systemtemperature is monitored via thermocouples at all T/C ports. In thecircuit diagram, the stages are electrically isolated by use ofelectrically insulating (e.g. Teflon®) tubing, or by Swagelok dielectricfittings. This provides electrical isolation of stage 1 from stage 2.

[0073] In single-stage compression, one electrochemical compressor unitis employed and, as examples of its performance, FIGS. 7 and 8 showtemporal plots for compression from atmospheric pressure (15.9 psia) toapprox. 45 and 75 psia hydrogen, respectively. FIGS. 9 and 10 showcorresponding temporal plots of the applied voltages along with thethermodynamic applied potential (ΔE) as determined from equation 4. Forcompression to 45 psia, 0.6 A was applied galvanostatically, and alinearly increase in pressure in the cathodic compartment (volume=18.2mL) was effected. At t=610 sec, the pressure reached 45.7 psia (FIG. 7),and the voltage applied during compression increased from 58.2 to 70.3mV (FIG. 9). The current source was then discontinued (i=0 A), and theequilibrium potential across the cell was measured with ★E_(cell)|=14.1mV. For compression to 75 psia, a linear pressure increase in thecathodic compartment also took place and, at t=1270 sec, P_(H) ₂_(,c)=76.4 psia. The applied voltage during compression increased from57.1 to 78.4 mV (FIG. 11). The current source was then discontinued, andthe equilibrium cell potential measured was |E_(cell)|=22.0 mV. In bothstudies, the system temperature recorded was 22.0° C. There is excellentagreement in the profile of the plots of the applied voltages and ΔE(E_(polarization)=58 mV), and between ΔE and the measured |E_(cell)|.For compression to 45 psia, the energy consumption, determined usingequation 8, was 25.1 J (with w_(t)=3.9 J). The efficiency, as determinedfrom equation 9, was 16%. For compression to 75 psia, w=56.1 J (withw_(t)=11.9 J), and the efficiency was 21%. It is noted that efficiencyimproves with increasing temperature and with decreasing applied current(due to lower i²R losses), and upwards of 80% has been reported forsingle-stage electrochemical compressors [4,5]. For the present system,compression to 45 psia at 65 and 80° C. with i=0.6 A yields the appliedvoltage profiles as illustrated in FIGS. 11 and 12 (E_(polarization)≈43mV at 65° C.; E_(polarization)=33 mV at 80° C.), and the respectiveefficiencies were 22 and 28%. Likewise, with i=0.1 A and T=65° C., theprofile of the applied voltage for compression to 45 psia is shown inFIG. 13 (E_(polarization)=7.8 mV), and the efficiency here was 60%.

[0074] In dual-stage compression, two electrochemical compressor unitsconnected in series are employed, and FIG. 14 shows an example of thepressure change at each stage (unit) from application of electricalpower. Here, 45 and 75 psia were chosen as final pressures for the firstand second stages, respectively, both stages initially at atmosphericpressure (15.9 psia). A current of 2.4 A was applied galvanostaticallyto stage 1 and 0.6 A to stage 2. A linear increase in pressure waseffected at both stages; 46.7 psia was reached at t=315 sec for stage 1(volume=27.2 mL), and 75.7 psia was attained after 1230 sec for stage 2(volume=18.2 mL). At stage 1, the current was reduced to 0.6 A tomaintain the pressure until the final pressure at stage 2 was reached.Afterwards, the current source was discontinued at both stages (i=0 A),and the equilibrium cell potential was measured at both stages, with|E_(cell)|=15.0 mV for stage 1 and |E_(cell)|=6.9 mV for stage 2.

[0075]FIG. 15 shows the temporal plots of the applied voltages withcomparison to those for ΔE (as determined from equation 4), and there isgood agreement of the profile of the plots (E_(polarization)=40 mV (0.6A) and 158 mV (2.4 A) for stage 1, and E_(polarization)=57 mV (0.6 A)for stage 2). The system temperature was 22.0° C. The energy consumptionfor priming the dual-stage compressor to the chosen stage pressures was400.7 J, as determined using equation 8.

[0076] Single-stage compression to higher pressures was also performed.For example, compression to 535 psia (FIG. 16) was carried out at T=22°C. and using i=0.6 A. The profile of the applied voltage is shown inFIG. 17, and there is good agreement with that of ΔE(E_(polarization)≈52 mV). The energy consumption, as determined from eq.8, was 362.4 J (with W_(t)=231.4 J), and the efficiency, as determinedfrom eq. 9, was 39%.

[0077] Dual-stage compression to higher to pressures has also beencarried out. For example, at T=22° C., compression to 2000 psia, withstage 1 at 1000 psia, is illustrated in FIG. 18. The profile of theapplied voltages is shown in FIG. 19, and there is good agreement withΔE derived from eq. 4. The applied current was 4.0 A for stage 1 and 2.0A for stage 2. The equilibrium cell potentials were |E_(cell)|=53.0 mVfor stage 1 and |E_(cell)|=8.7 mV for stage 2.

[0078] For the fuel cell industry, the electrochemical hydrogencompressor can be applied interfacing: 1) a hydrogen production device(i.e. fuel processor, electrolyzer, etc.) and a fuel cell; 2) a hydrogenproduction device and a hydrogen storage device; and 3) a hydrogenstorage device and a fuel cell. For industries concerned with hydrogensupply and storage, the compressor can be applied interfacing a hydrogenproduction device and a hydrogen storage device.

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[0088] 10. Eberle, K., Rohland, B., Scholta, J., Ströbel, R.; U.S. Pat.No. 6,361,896, 2002.

1. An apparatus for compression of hydrogen, comprising a membraneelectrolyte cell assembly (MEA), including a proton-conductingelectrolyte membrane, an anode on one side of the membrane and a cathodeon the other side of the membrane, the anode having an electrochemicallyactive material for oxidizing hydrogen to protons, the cathode having anelectrochemically active material for reducing protons to hydrogen, andfurther comprising next to the anode and cathode, planar gasdistribution and support plates sandwiching the MEA, the assembly beingheld together by end-plates, the end-plates having complementaryperipheral grooves for seating an intervening seal between theend-plates and the MEA, the end-plate on the anode side furtherincluding a hydrogen supply inlet and the end-plate on the cathode sidefurther including a compressed hydrogen outlet.
 2. The apparatusaccording to claim 1, wherein the gas distribution and support platesinclude a central gas distribution area.
 3. The apparatus according toclaim 2, wherein the gas distribution area is in the form of pores. 4.The apparatus according to claim 1, the gas distribution and supportplates are made of a porous sintered metal frit material.
 5. Theapparatus according to claim 4, wherein the metal frit is stainlesssteel frit.
 6. The apparatus according to claim 2, wherein theend-plates each include an additional complementary pocket for seatingthe metal frit plates.
 7. The apparatus according to claim 6,additionally comprising on the cathode side between the gas distributionand support plate and the end plate, a spring means for ensuringadequate electrical contact.
 8. The apparatus according to claim 7,wherein both the spring and spring support are made of stainless steel.9. The apparatus according to claim 7, wherein the proton conductingmembrane is of a material selected from the group consisting of Nafion®,sulfonated-polystyrene and the partially fluorinated ionomericmembranes, lonClad® R-1010 and R-4010.
 10. The apparatus according toclaim 1, additionally comprising means for applying an electricpotential to the cell, wherein the applied potential to effect a finalpressure of hydrogen exiting the cathode side of the cell is determinedby the Nernst equation.
 11. The apparatus according to claim 1,comprising a plurality of MEA cells connected in series, such that thecompressed hydrogen from the hydrogen outlet of a first cell in theseries is fed to the hydrogen inlet of the next cell in series, whereineach cell is electrically isolated from the next cell in the series. 12.A process for the compression of hydrogen by means of the apparatusaccording to claim 1, wherein hydrogen is compressed electrochemicallyby the MEA by oxidation of the hydrogen to protons at the anode, whichhaving passed through the membrane to the cathode side are reduced backto hydrogen and discharged under pressure.
 13. The process according toclaim 12, wherein hydrogen is pressurized to 12,000 psi or greater. 14.The process according to claim 12, wherein a plurality of MEA cells areconnected in series, each cell being electrically isolated from the nextcell in the series, such that hydrogen discharged under pressure fromthe hydrogen outlet of a first cell in the series is fed to the hydrogeninlet of the next cell in series, and hydrogen is discharged from thehydrogen outlet of the next cell at a higher pressure.
 15. An apparatusfor compression of hydrogen, comprising a membrane electrolyte cellassembly (MEA), including a proton-conducting electrolyte membrane, ananode on one side of the membrane and a cathode on the other side of themembrane, the anode having an electrochemically active material foroxidizing hydrogen to protons, the cathode having an electrochemicallyactive material for reducing protons to hydrogen, and further a hydrogensupply inlet and a compressed hydrogen outlet.